The capabilities of image sensors are constantly getting better, also in the area of the ubiquitous small smartphone sensors. Sony has developed a new 3-layer stacked high speed CMOS sensor with DRAM. It promises to minimise image distortion and add super slow motion capabilities to future smartphones.
Sony announced the development of the industry’s first 3-layer stacked CMOS sensor for smartphones. Compared to traditional 2-layer sensors, the new Sony sensor features an added DRAM layer. The purpose of this extra layer is to increase data readout speeds and make it possible to capture still images of fast-moving subjects with minimal focal plane distortion (something we also call “rolling shutter”) as well as super slow motion movies at up to 1,000 frames per second in 1080p.
Sony also claims to have found solutions for various technical problems inherent in the design, such as reducing the noise generated between the circuits on each of the three layers.
Conventional 2-layer stacked CMOS sensor vs New 3-layer stacked CMOS sensor. Source: Sony
The DRAM layer temporarily stores image signals from pixels, enabling data to be processed at an optimal speed for the standard specifications. I understand this new layer as a kind of improved buffer that allows the system to read the whole 19.3 megapixel still image in only 1/120 of a second, or around 4 times faster than conventional 2-layer sensors. This brings two great features.
1. Minimizing focal plane distortion / rolling shutter
Thanks to the DRAM layer and a super fast 1/120 second readout, the focal plane distortion – also known as rolling shutter effect – is minimized as it takes approximately 4x less time to read the whole line of pixels. Therefore, we should see less rolling shutter with this sensor in the future.
1/30 second sensor readout (left) vs 1/120 second sensor readout (right). Source: Sony
2. Capturing super slow motion clips
Another cool feature of the new high speed CMOS sensor is the ability to capture super slow motion clips at up to 1.000 frames per second in full HD (1920 x 1080 pixels). To ensure users will not miss interesting moments, it is possible to start high speed recording automatically with the detection of sudden movement of a subject. Because high speed shooting data is first stored on the DRAM and then sent further at a normal speed, a conventional image signal processor can be used. You can take a look at the demonstration video below. I personally find it a little bit weird that there is only a playback of 15fps with these super slow motion segments, although they still look good.
Key specifications of the new high speed CMOS sensor:
Resolution: 5520 x 3840 pixels (21.2 mp)
Sensor size: 1/2.3 (7.73mm diagonal)
Unit cell size: 1.22μm x 1.22μm
Reading speed is 8.478 ms (4:3 19.3 Mpx) / 6.962 ms (16:9 17.1 Mpx)
DRAM capacity is 1 Gbit
You can find more information in the original press release on the Sony website. But the question remains: when will we be seeing this new sensor implemented in smartphones and what will be the final specifications and software limitations?